1. Field of the Invention
The present invention, in wire bonder performing an assembling process of semiconductor package, relates to an apparatus for moving a bonding head of a wire bonder in X, Y and Z axial directions and a method for controlling position of the bonding head in order to perform a wire bonding on an objective bonding position.
2. Description of Related Art
Generally, in a wire bonder, there is an apparatus for moving a bonding head, which performs a wire bonding to connect a lead with a pad, to an objective bonding position by moving a X, Y and Z tables.
Hereinafter, an apparatus for moving a bonding head of wire bonder of a prior art will be schematically described, referring to FIGS. 1 and 1A.
FIG. 1 is a perspective view showing apparatus for moving a bonding head of wire bonder, in X and Y axial directions, of a prior art.
As shown in FIG. 1, the apparatus for moving a bonding head of the prior art comprises a stage 100 having a tenon 100a longitudinally (i.e., in the X axial direction) formed on bottom portion and a pair of supporting members 102 protruded from both sides of an end thereof, a X table 104 having a linear motor (not shown) for providing a force moving longitudinally the stage 100 inside thereof and a tenon 104a longitudinally formed on bottom portion, an X base 106 having a groove 106a for receiving the tenon 104a of the X table 104 and guiding the X table 104 to be longitudinally moved, a Y table 108 having a linear motor (not shown) for providing a force moving transversely (i.e., in the Y axial direction) the stage 100 inside thereof, a groove 108a for guiding the stage 100 and a tenon 108b transversely formed on bottom portion, a Y base 110 having a groove 110a for receiving the tenon 108b of the Y table 108 and guiding the Y table 108 to be transversely moved, a moving bar 112 jointed to the supporting members 102 in order to move transversely the stage 100, a bearing 114 arranged on both sides of the moving bar 112, and a bracket 116 for fixing the bearing 114.
Further, each of the grooves has a plurality of holes (not shown) for providing air pressure inside thereof so that the tenons 100a, 104a and 108b of stage 100, X table 104 and Y table 108 can be moved in longitudinal or transversal direction in state that they are apart from the grooves.
When sub-driving portion supplies a control signal to the linear motors in order to control position, direction and angle of the bonding head, each of the linear motors moves rapidly the X and Y tables in a short motion section.
Hereinafter, operation of the apparatus as mentioned above will be schematically described.
In the state that the bonding head is disposed on the stage 100, when the linear motors disposed inside of X and Y tables 104 and 108 are operated, the X table 104 is moved along the groove 106a. Therefore, the stage 100 is longitudinally moved along the groove 108a. Also, the Y table 108 is tranversely moved along the groove 110a formed on the Y base 110 transversely. At this time, since the tenon 100a is received on the groove 108a, the stage 100 is transversely moved along with the Y table 108 and the moving bar 112 is transversely moved in the state contacted to the bearing 114.
In the apparatus, since the moving bar is moved in the state contacted to the bearing, it is difficult to increase velocity of the stage 100 to be moved. In addition, since the bearing is worn by a friction between it and the stage, there is a problem that maintenance of the bearing is required often.
FIG. 1A illustrates a motion character of the X and Y tables by operation of the linear motors.
As shown in FIG. 1A, since a converter changing a rotary force to linear force by means of a cam is used for transferring a mechanical power of motor to the stage, the mechanical power is applied to position offset from the centroid of ths stage "Cm (Xm, Ym, Zm)". Therefore, since unnecessary moments such as pitching moment "Mx" rolling moment "My" and yawing moment "Mz" causes in the stage, the life of stage is reduced and the entire volumne of apparatus is increased.
In the prior art, an apparatus for moving the bonding head in the Z axial direction moves finely a capillary, which is moved to a bonding position by motion of the stage, in the vertical direction in order to perform the wire bonding by operation of the bonding head.
The apparatus for moving the bonding head in the Z axial direction comprises a rotary servo motor providing a control signal to the linear motors in order to control position, direction and angle of the bonding head, an eccentric-driven cam and a moving block, which has a bearing, for converting a rotary motion into a vertical motion, and an encoder for sensing a rotation angle of the moving block. In this case, the capillary is finely moved by signal outputted from the encoder and performs the wire bonding.
Hereinafter, the apparatus of the prior art will be schematically described how the apparatus operates.
When the X and Y tables are moved by operation of the linear motors and the bonding head is moved to a bonding position, the rotary servo motor is rotated by required value, and the moving block is moved by the eccentric-drived cam in the vertical direction. Therefore, the capillary performs a wire bonding to connect lead to pad.
In the apparatus of the prior art as mentioned above, each of the linear motors have a cylindrical coil or a flat type magnet mainly. When the linear motor consists of the former cylindrical coil, it is difficult that the bonding head is rapidly moved because the apparatus is large and heavy than the other apparatus having a similar features. Also, when the linear motor has the latter flat type magnet, since hysterisis causes in a section which a small power is offerred, the apparatus needs additional device for retaining uniformly the power. Further, during moving, there is a problem that the X and Y tables may be shocked mechanically.
Furthermore, when a rotary servo motor is used as a power source of the apparatus, a device for converting motion, for example such as ball screw, coupling and so on, is required, and disassemble and assemble are difficult because the elements are many. More particularly, since all the positions of the bonding head in the X, Y and Z axes should be converted by means of the rotary servo motor, it is difficult that a final position of the stage is sensed accurately.